So, I wanted to re-try tightening the rear ground strap. And guess what, it worked! I no longer have any whine! Thanks to
@camalaio for trying this and posting it.
Just to recap, I had a whine from 38mph to 52mph, with two peaks at 38 and 48mph. I wanted to try tightening the rear strap first, then the front strap later, to see if I could help ID where the whine was coming from.
I removed the one end, the easily reachable one, from the rear braided ground strap. Takes no time at all after removing the rear driver-side tire. Cleaned it, and retightened. My whine improved, as the range was smaller, 41mph to 45mph, and now only a single peak around 42mph.
After a few weeks, I did the front, but the front solid ground strap was hard to reach, and so I only tightened it. The sound had no change. Interesting that it was the rear braided strap and not the front solid strap that made some difference.
Now, with the weather cold, I wasn't too interested in re-doing the rear strap, but today, the temps warmed up, and so I redid the rear strap, MUCH tighter and gave it a squirt of anti-corrosion spray for good measure. And guess what? The whine is completely gone! So, happy that this simple fix worked. Honestly, now that I've done it, I think it might only take 15mins. Lift your rear driver side tire, remove it, the strap nut is easily reachable, remove that, clean it, reattach MUCH tighter, and put the wheel back on. Honestly, it's little more than changing a tire. 15 to 20mins.
Thank you, camalaio!
I'm just annoyed I didn't fix this correctly the first time, but I read that TSB where it sounded like you shouldn't over tighten the nut. The steps first had you "hand-tighten" the nut. Then you tightened it to 10NM, which is not that tight. In the end, I tightened it considerably more tight. Maybe that's why some of us have the whine, 10NM is not tight enough?